Positional Isomerism Controls Polarity and Nonlinear Optical Properties in One-Dimensional Hybrid Germanium Halides.

being primarily attributed to the asymmetric electron distribution arising from N1-methyl substitution that enables the favorable ordered alignment of the π-conjugated 1-Mim. Our findings not only highlight the critical role of cation positional isomers in controlling physical properties in one-dimensional hybrid perovskites but also establish one-dimensional germanium-iodide perovskites as promising lead-free candidates for nonlinear optoelectronic applications.